Ultra high frequency tuner having rectilinearly sliding plates providing variable inductance and capacitance



Nov. 10, 1964 H. T. LYMAN ETAL 3,156,884

ULTRA HIGH FREQUENCY TUNER HAVING RECTILINEARLY SLIDING PLATES PROVIDINGVARIABLE INDUCTANCE AND CAPACITANCE Filed April 50, 1962 5 Sheets-Sheet1 T F1 Z MD b Harold J'.' Lyman Hands 6. Mason Jesse C. Ja ua INVENTOQMAQAQ 222 MM I CZ'ZZys Nov. 10, 1964 H. T. LYMAN ETAL 8 ULTRA HIGHFREQUENCY TUNER HAVING RECTILINEARLY SLIDING PLATES PROVIDING VARIABLEINDUCTANCE AND CAPACITANCE Filed April 50, 1962 5 sh s 2 [5gb IIIIIIUII5 minim M lszb 15:2 I A I05 I lv I00 1 \o 14m 74: 6)] 14m Us 792% W [l-18 I824: lg 2, I 1

' 20 I In! hi- 6 9 52 z "-214- hirrolcl I Lym n 6 -24! 715N225 FrancisGMason 20z--";i Jesse C. Jaguq /242 INVENTORS E I v HIGH- CIRCUIT BY w ET I p FIG. 1 3

Nov. 10, 1964 H. T. LYMAN ETAL 3,156,884

ULTRA HIGH FREQUENCY TUNER HAVING RECTILINEARLY SLIDING PLATES PROVIDINGVARIABLE INDUCTANCE AND CAPACITANCE Filed April 50, 1962 5 Sheets-Sheet5 FIG 11 [Jim 6 1921 W/ 204 2/2 leg; 2

i C/ecu/T FIG. 12

Harold I Lyman fiancis 6, Mason Jesse C. Jac ua INVENTORS l I lam FIG.10

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NOV. 10, 1964 HA rr- 3,F1 5"6 ,'i8.84

ULTRA HIGH EREQUEINCY TUNER 'H'AVING RECTILTNEARLY SLIDING PLATESPROVIDING VARIABLE INDUCTANCE ,AND CAPACITANCE :Filed April 50, 1962 5\sheeibs sheevt 4 FIG.

7 54 lg M 52 Harold I Lyman Franczs 6. Mason 42 Jesse CZJaqu L W? ['j WINVENTORS k 1 BY M M M .z" W

3,156,884 I IDIN H. T. LYMAN ETAL NCY TUNER HAVING R Nov. 10, 1964 ULTRAHIGH FREQUE ECTILINEARLY SL. G PLATES PROVIDING VARIABLE INDUCTANCE ANDCAPACITANCE Filed April 30, 1962 5 Sheets-Sheet 5 Common M0zion FIG. 15

Harold T. Lyman. fiancis GMason Jessie Q Jagua I N V E N T0 5 3,156,384ULTRA HIGH FREQUENQY TUNER HAVING REC- TlLINEA-RLY PLATES PRGVIDINGVAIHABLE INDUQTANIIE AND (JAPACITANCE Harold 'I. Lyman, Milford, FrancisG. Mason, Weston, and lesse 6S. .laqua, New Haven, Conn, assignors toAladdin Industries, Incorporated, Nashville, Tenn., a corporation oflllinois Filed Apr. 30, I962, Ser. No. 190,881 4 tllalms. (Ci. 334-68)This invention relates to tuners, particularly for ultra high frequency(UHF) applications, such as radio and television receivers and otherequipment.

One object of the present invention is to provide a new and improvedtuner having a tuned circuit, especially suitable for use in anoscillator, in which both the inductance and the capacitance are Variedin a novel manner. In this way, the tuner provides an extremely widerange of frequency coverage.

A further object is to provide a new and improved tuner of the foregoingcharacter which is extremely small and compact and reasonably low incost.

Another object is to provide a new and improved arrangement, in a tunerfor a superheterodyne receiver, whereby a pickup conductor is employedto transfer energy from the superheterodyne oscillator to thesuperheterodyne mixer, While overcoming the effect of unwantedresonances in the pickup conductor.

it is another object to provide a tuner having a new and improvedtracking arrangement, whereby the tuning 9 curve of the tuner may bevaried at a multiplicity of points in the tuning range, so that thetuning curve may be brought into a desired relationship with anothertuning curve, or with the calibration of a dial or the like.

A further object is to provide a new and improved tracking arrangementof the foregoing character in which the tracking arrangement is appliedto a tuner of the variable cavity type.

Another object is to provide such a new and improved trackingarrangement which utilizes a fine tuning member adapted to be operatedby a selectively adjustable camming mechanism operable by the drive forthe main tuning member.

Further objects and advantages of the present invention will appear fromthe following description, taken with the accompanying drawings, inwhich:

FIG. 1 is a plan view showing the top of a superheterodyne UHF tuner tobe described as anillustrative embodiment of the present invention.

FIG. 2 is a side elevational view, taken generally as indicated by theline 2-2 in FIG. 1.

FIG. 3 is an elevational View of the opposite side, taken generally asindicated by the line 3-3 in FIG. 1.

FIG. 4 is a front elevational view taken generally as indicated by theline 4-4 in FIG. 3.

FIG. 5 is a rear elevational view, taken generally as indicated by theline 5-5 in FIG. 3.

FIG. 6 is an enlarged somewhat diagrammatic crosssectional view takengenerally along the broken line 6-6 in FIG. 2.

FIG. 7 is a somewhat diagrammatic horizontal section, taken generallyalong the line 7-7 in FIG. 2.

FIG. 8 is an elevational section, taken generally along the line (3-8 inFIG. 6.

FIG. 9 is a somewhat diagrammatic developed view showing details of oneof the tuning elements employed in the tuner.

FIG. 10 is a fragmentary elevational view, taken generally as indicatedby the line iii-10 in FIG. 2.

FIG. 11 is a fragmentary elevational view, taken generally as indicatedby the line 11-11 in FIG. 2.

nited States Patent 0 3,15%,884 Patented Nov. 10, 1964 ice FIG. 12 is adiagram representing the approximate equivalent circuit of the tuner forthe low frequency portion of the tuning range.

FIG. 13 is a diagram representing the approximate equivalent circuit forthe high frequency end of the tuning range.

FIG. 14 is a fragmentary greatly enlarged cross-sectional view takengenerally along the line 14-14 in FIG. 8.

FIG. 15 is a fragmentary exploded perspective View showing thestationary and movable tuning plates and associated components of thetuner, the movable plates being separated upwardly from the. stationaryplates for clarity of illustration.

It will be understood by those skilled in the art that the invention maybe applied to radio and television receivers and various other types ofhigh frequency equipment. Thus, it is merely by way of example that theillustrative embodiment shown in the drawings takes the form of asuperheterodyne tuning unit 2 intended for use in connection with aradio or television receiver in the ultra high frequency range. Thetuning unit 2 is capable of covering an extremely wide tuning range,which, for

example, may extend from 300 to 1,000 megacycles per second.

The illustrated tuning unit 2 comprises a superheterodyne localoscillator 4 which utilizes an electronic oscillation generating device,such as the illustrated triode vacuum tube 6, for example. A signal fromthe oscillater 4 is fed into a superheterodyne mixer 8. In this case,the mixer 3 utilizes a crystal diode or rectifier 9. The incoming radioor television signals are also fed to the mixer 8, through two radiofrequency tuner sections or preselector stages 12a and 12b.

Various features of the tuner sections 12a and 1215 are in accordancewith the invention disclosed and claimed in the co-pending applicationof Francis G. Mason, Serial No. 143,343, filed October 6, 1961. Thetuner sections 12a and 12b are quite similar in construction. Thus, forthe most part, the following description will be directed to the firsttuner stage 12a. The second tuner stage 12b may be considered to be thesame, except as otherwise specifically indicated.

The illustrated tuner section 12a is of the cavity type and thuscomprises a conductive metal body 14 (FIGS. 6, 7 and 8) which is formedwith an internal cavity or chamber 16. The body 14 may be in the form ofa metal casting 18, having a cover plate 20 secured to one side thereof.In this case, the cavity 16 is rectangular in shape, but any othersuitable shape may be utilized. Thus, the cavity 16 is bounded by endwalls 22 and 24, side walls 26 and 28, a top wall 30, and a bottom wall32. In this case, the bottom wall 32 is formed by the cover plate 20.The side wall 26 is in the form of a partition between the cavities ofthe first and second tuner sections 12a and 12b.

The illustrated cavity tuner section 12a is of the re-entrant type andthus is provided with a center post 34 which extends longitudinally inthe cavity 16.. As shown, the center post 34 takes the form of twooverlapping sections or members 36 and 38 (FIGS. 8 and 9) which areconnected to opposite end walls of the body 14. In this case, theoverlapping portions 36 and 33 are connected to the end walls 22 and 24,respectively.

In order that the tuner may be made with a high degree of precision, yetat moderate cost, the two portions 36 and 33 of the center post 34 arepreferably formed as thin patterned metal coatings or members on acylinder or rod 40 (FIG. 14), which may be made of a suitable insulatingmaterial, such as steatite, glass, or various other ceramic or plasticmaterials. The metal coatings or 419 members which make up the centerpost sections 36 and 38 may be applied to or formed on the insulatingmember 40 in the desired patterns by the utilization of wellknown'printed circuit techniques.

A gap or band 42 (FIGS. 8 and 9) of the insulating material is providedbetween the overlapping sections 36 and 38. It will be seen that thecenter post section 36 extends from a conductive cylindrical member 44which is connected to the end wall 22. Similarly, the section 38 extendsfrom a conductive cylindrical member 46 which is connected to the endwall 24. The section 36 is disposed on one side portion of thecylindrical insulating member 40, while the section 38 is disposed onthe opposite side portion thereof. The section 36 projects toward theend wall 24 but is insulated therefrom. Similarly, the section 38projects toward the end wall 22 but is insulated therefrom.

Input and output connections may be made to the cavity sections 12a and12b in any known or suitable manner. Various input and output elementsare well known to those skilled in the art. In the illustrated tuner 10,an input connection is made to the initial tuner section 12a by means ofa coupling loop 48 which is connected between an input terminal 50 andthe cover plate 20 of the body 14; A connector 52 may be mounted on theplate 20 for the purpose of connecting the input terminal 50 to acoaxial input cable. It will be seen that the loop 48 is disposedlongitudinally in the cavity 16, at one end thereof, adjacent the endwall 22 and the center post section 36. With this arrangement, themagnetic field in the cavity is strongest in the end portion of thecavity adjacent the loop 48.

In the illustrated arrangement, energy is coupled between the cavitysections 12a and 1212 by means of a slot 54 which is formed in thepartition 26, at the end of the cavity-adjacent the end wall 22 and theloop 48. The slot 54 permits magnetic interlinkage between the tunersections 12a and 12b so that signals will be magnetically coupledtherebetween.

The output from the second cavity section 12b may be taken by means of asecond coupling loop 56 which is similar to the loop 48 but 'isconnected between one end 22 of the cavity section 1217 and an outputlead 58. As shown, the output lead 58 extends through a small opening'60 in the side wall 28 and is connected to the diode rectifier 9,employed in the superheterodyne mixer 8.

The resonant frequency of the illustrated tuner section 12a is varied bymoving an electrode 66 along the center post 34. As shown, the electrode66 takes the form of a conductive metal sleeve or cylinder which isslidably received around the center post 34. Outward projecting flanges68 and 70 are formed on the opposite ends of sleeve 66.

An insulating layer or space is provided between the sleeve 66 and thecenter post 34 so that the sleeve will be capacitively coupled to thecenter post sections 36 and 38. takes the form of a thin coating 72(FIG. 14) of insulating material on the outside of the center post 34.The coatingconveniently may be applied to all of the exposed outersurfaces of the portions 36, 38,40, 44 and 46. It Will be realized thatan insulating film might alternatively be applied to the inside of thesleeve 66. The insulating layer may be made of any suitable low-lossplastic material, such as Teflon, which has the particular advantage ofreducing the friction between the sleeve '66 and the center post. I

The movement of the sleeve 66 has the eifect of varying the capacitancebetween the center post sections 36 and 38. This in turn has the effectof varying the resonant frequency of the cavity tuner section. As shownin FIG. 8, the sleeve 66 almost completely surrounds both center postsections 36 and 38. This represents approximately the position ofmaximum capacitive con- In the illustrated construction, the insulatinglayer pling between the sections 36 and 38. Thus, the position of thesleeve 66, as shown in FIG. 8, represents approximately the lowfrequency end of the tuning range. It will be understood that the sleeve66 is capacitively coupled to both center post sections 36 and 38 andthus is the means of establishing increased capacitive coupling betweenthe center post sections.

The sleeve 66 may be moved to the left, as seen in FIG. 8, so as todisengage the sleeve in a progressive manner from the center postsection 38. Such movement of the sleeve reduces the capacitance betweenthe center post sections 36 and 38. In its position of extreme movementto the left, the sleeve 66 is received around the cylindrical conductor44 so that the capacitive coupling between the center post sections 36and 38 is at a minimum. This position represents the extreme highfrequency end of the tuning range.

To provide for the desired movement of the sleeve 66, the tuner 10 isprovided with a precision lead screw '74 (FIG. 1) which may be rotatedby any suitable drive. A traveling nut 76 (FIG. 6) is threaded onto thelead screw 74 and is prevented from rotating by means of a guide rod 78.It will be seen that the nut 76 is formed with arms or fingers 80 whichengages the upper side portion of the guide rod 78. The lower sideportion of the rod 78 may be engaged by anti-friction pads 82 (FIG. 2)on the outer ends of leaf springs 84 which are mounted on the undersideof the nut 76. The rod 78 is also engaged by an anti-friction pad 83(FIG. 1) on the free end of a leaf spring 85, mounted on the side of thenut 76.

The illustrated nut 76 has a downwardly projecting tongue 86 (FIG. 6)adapted to operate a movable carriage 88 on which the sleeves 66 aremounted. In this case, a bow-shaped leaf spring 90 (FIG. 8) is employedto connect each sleeve 66 to the carriage 88. The ends of spring 90 areconnected to the flanges 68 and 78 on the sleeve 66. The center portionof the spring 99 is connected to an insulating block 92 which is securedto the underside of the carriage 88. Thus, the sleeve 66 is insulatedfrom the carriage 88. No external electrical connection is made to thesleeve 66.

In the illustrated construction, the tongue 86 extends into a slot 94formed in the carriage S8. A ball 96 may be interposed between one sideof the slot 94 and the tongue 86. The other side of the tongue may beengaged by a spring-pressed pin 98 mounted in the carriage 88.

As shown to advantage in FIG. 6, one end portion of the illustratedcarriage 88 is formed on its underside With a V-shaped groove 18%) whichis slidable along a stationary V-shaped way or slide 102. In this way,the carriage is constrained to slide along a straight line path. Theother end of the carriage 88 is guided by an upwardly facing flatsurface or way 184 which may be provided on the upper side of thecasting 18. The carriage 88 may be fitted with an anti-friction pad 186,adapted to slide along the flat surface 104.

The springs 90 of the cavity sections 12a and 1215 have the effect ofpulling the carriage 88 downwardly against the fiat guiding surface 184.At the same time the springs 90 provide uniform upward pressure on thesleeves 66 so that the sleeves will slide easily along the center post34. To provide additional spring pressure between the carriage 88 andthe V-shaped way 102, a leaf spring 1% is mounted on the carriage. Theouter end of the leaf spring 188 is provided with an anti-friction padwhich engages the underside portion of the guide rod 78.

The illustrated drive arrangements eliminates any play or binding effectbetween the various movable elements, of the drive, so that the sleeves66 may be translated easily and with a high degree of precision. Theillustrated drive reduces backlash to such an extent that it isvirtually negligible. Thus, the tuner may be reset to.

a desired position with an extremely high degree of precision.

As previously indicated the movement of the sleeve 66 along the centerpost 34 changes the amount of capacitance between the center postsections 36 and 38. In this way, the resonant frequency of the tunercavity section is varied. An extremely wide range of frequencies may becovered. Thus, the range from 315 to 1000 megacycles may be covered withonly about 2 /2 inches of sleeve travel.

The illustrated cavity tuner construction is highly eflicientelectrically. It has been found that unloaded Q values in the range from700 to 1100 can readily be obtained.

The tuner sections 12a and 12b are provided with tracking mechanisms 116(FIG. 5) so that the tuner secions may be tracked accurately with theoscillator 4, or with a predetermined dial calibration or other tuningcurve. As shown to advantage in FIG. 7, each of the tracking mechanisms116 comprises a fine tuning member or electrode 118 which is movablerelative to the overlapping sections 36 and 38 of the center post 34. Inthis case, the fine tuning electrode 118 is rotatable within theinsulating tube 40 which supports the center post sections 36 and 38.The fine tuning electrode 118 is similar in shape to one of the centerpost sections 36 and 38, in this case the section 36. As the electrode113 is rotated, it is moved into and out of alignment with the centerpost section 36. When the electrode 118 is aligned with the section 36,the electrode 118 has little or no effect upon the capacitance betweenthe sections 36 and 38. When the electrode 118 is moved out of alignmentwith the section 36, it progressively overlaps the section 33, so as tocause an increase in the capacitance between the sections 36 and 33.

It will be seen from FIG. 7 that the fine tuning electrode M5 isgenerally semi-cylindrical in shape and is supported on one side portionof a cylindrical rod 120, made of electrically insulating material. Itwill be noted that the electrode lib tapers toward its outer end. Theinner end portion of the electrode 113 is formed into a continuouscylindrical band 122 which is disposed with in the cylindrical portion44 of the center post section 36. Preferably, the electrode 118,together with its cylindrical inner portion 122, is formed as aconductive coating on the insulating rod 129. The coating may be appliedby any known or suitable printed circuit techniques.

The relationship of the fine tuning electrode 118 to the center postsections 3d and 38 is shown to good advantage in H6. 9, which is adeveloped view of the sections 36 and 38 and the electrode 118, rolledout into a flat plane. In FlG. 9, the electrode 118 is shown in theposition in which it overlaps the center post section 38 to the maximumpossible extent, so as to cause the maximum increase in the capacitancebetween the sections 36 and 38. It will be realized that the electrode118 is capacitatively coupled to both center post sections 36 and 38. Noexternal electrical connection is made to the electrode 118.

The insulating material of the tube 4%? acts as a dielectric between theelectrode 118 and the center post sections 36 and 38 so as to increasethe efiectiveness of the electrode 118. Thus, the rotation of theelectrode 118 may change the resonant frequency of the tuner by as muchas 10%. In this way, an unusually wide range of tracking adjustment isprovided.

The tracking mechanisms 116 provide adjustable means whereby the finetuning electrodes 118 of both tuner sections 12a and 12b may beselectively rotated in response to the operation of the main drivingmechanism. Thus, each tracking mechanism 116 comprises adjustablecamming means 126 (FIGS. 3-6), adapted to be moved by the main drivingmechanism. In this case, each camming arrangement 126 comprises aplurality of adjustable screws I128 which are threaded through a plate130 secured to the traveling nut 76. The camming screws 128 of each setproject downwardly through the plate 13% and are engageable with amovable cam follower. For clarity, the cam follower for the first tunersection will be referred to as 132a, while the cam follower for thesecond tuner section 12b will be referred to as 13217. As shown toadvantage in FIG. 3, the cam followers l32a and 1321) have generallysemi-cylindrical upper surfaces 134:: and 134b, so as to slide easilyalong the lower ends of the closely spaced carnming screws 123. The camfollowers 132a and 1252b are secured to rotatable shafts 136a and 136b,which are thus adapted to be rotated through limited angles by theaction of the camming screws 1%. Springs 133a and 1381) (FIG. 6) areconnected to the shafts i365! and i361) and are arranged to bias the camfollowers 132a and 13211 upwardly against the carnming screws 128.

The shafts 136a and 136!) are connected or linked to the fine tuningelectrodes 118 so that rotation of the shafts will cause the electrodesto be rotated. In this case, gear sectors 149a and 1463b are secured tothe shafts 136a and 13Gb. As clearly shown in FIGS. 4 and 5, the gearsectors 14% and 14% are on opposite ends of the shafts than and 13612.The gear sectors 140a and 14% mesh with gears or pinions 142a and 14215,mounted on the rotatable rods 120 which support the fine tuningelectrodes 11?: of the tuner sections 12:: and 12b. The gears 142a and142i) are on opposite ends of the rods 12 The rods 129 are provided withcollars or retainers 144a and 1445, on the ends thereof opposite fromthe respective gears 142a and 142k.

It will be understood that the camming screws 128 may be adjusted sothat their lower ends lie in the same horizontal plane. In that case,the corresponding cam followers 132a and 1321; will not be moved to anysignificant extent as the traveling nut 76 is translated throughout itsrange of travel. For this adjustment of the screws 128, there will be nomovement of the tracking electrodes 113. Normally, however, it will benecessary to make tracking adjustments by adjusting the screws 3128 todifferent positions, as shown to advantage in FIG. 3. In that case, thecam followers 132a and 13211 will follow the lower ends of the screws asthe nut 76 is translated. Thus, the cam followers 132a and 132/; will berocked or swung to various positions. The gear sectors 140a and 3.461)and the gears 142a and 1421) transmit and amplify the swinging movementof the cam followers 132a and 13%, so that the tracking electrodes 1T8are rotated through angles considerably greater than the movement of thecam followers. Thus, considerable changes in the tracking of the tunersections 12a and 121) may be made by adjusting the camming screws 128.Inasmuch as there are a multiplicity of camming screws 123 in each ofthe camming sets 126, the tracking may be adjusted at a multiplicity ofpoints throughout the tuning range.

Each of the tuner sections 12a and 12b is also provided with asupplemental or auxiliary tracking arrangement (FIG. 6), comprising amultiplicity of electrodes 152 which are movable into capacitativecoupling with the tuning sleeve 66. In this case, the electrodes 152take the form of spring leaves or blades which are mounted on the lowerwall 32 of the cavity 16. Thus, the electrodes 152 are grounded to theouter housing 18 of the cavity. As shown in FIG. 3, the electrodes 152are distributed along the path of movement of the tuning sleeve 66. Aflange or lug 154' projects downwardly from one end of the sleeve 66 toestablish the capacitive coupling with the electrodes 152. Eachelectrode spring 152 may be provided with a screw 156, threaded throughthe lower wall 32, for adjusting the position of the spring. However,some of the screws 156 may be removed or omitted, if not needed toachieve the desired tracking adjustment. Inititally, each electrodespring 152 is biased by its own resiliency to its lowermost position,remotely spaced from the flange 154. By inserting the correspondingscrew 156 and screwing it upwardly, the spring 152 may be swung upwardlyinto closely spaced relationship with the flange 154. Actual contactbetween the springs 152 and the flange 154 must be avoided to preventthe tuning sleeve 66 from being grounded. In FIG. 8, the trackingsprings 152 are shown in various positions of adjustment.

The oscillator 4 has a tuned circuit 16% which is arranged so that boththe inductance and the capacitance in the circuit may be simultaneouslyvaried. In this way the variable tuned circuit 169 is enabled to coveran extremely wide frequency range. As previously indicated, theillustrated oscillator 4 utilizes an oscillation generating device inthe form of a triode vacuum tube 6 having a cathode 162, a grid 164 anda plate or anode 166. In this case, the tuned circuit 160 is connectedbetween the grid 164 and the plate 166, as shown to advantage in FIG. 6.

The illustrated tuned circuit 16% comprises a pair of parallelconductive bars 168 and 17% which are in the nature of parallel lineconductors. The bars are spaced apart and are mounted on an insulatingsupport 172. In this case, the bar 168 has an inner end portion 168a andan outer end portion 16812. It will be seen from FIG. 2 that the outerend portion 1653b is offset upwardly from the inner end portion 168a. Aslanting or diagonal portion 168cextends between the portions 168a and16%. Similarly, the bar 170 has inner and outer end portions 170a and170]). The outer portions 16811 and 17019 are spaced apart the samedistance as the inner portions 168a and 1719a, all of such portionsbeing substantially parallel to one'another. It will be apparent fromFIGS. 2 and 6 that the grid 164 and the plate 166 are connected to theinner end portions 168a and 170a, by means of straps or other conductors174 and 176 extending downwardly through openings 178 and 189 in theinsulating support 172. The bar 170 is entirely insulated from the bar168.

To provide for variation of the inductance and capacitance of the tunedcircuit 160, two sets of capacitive coupling plates are mounted on eachof the bars 168 and 170. Thus, an inner set of plates 182a is mounted onthe inner end portion 168a of the bar 168. Similarly, an inner set ofplates 184a is mounted on the inner end portion 170a of the bar 17%.Outer sets of plates 182i) and 18% are mounted on the outer end portions1623b and 17% of the bars 168 and 171). All of the plates 182a, 182b,184a and 1234b extend vertically and are substantially parallel to oneanother. As shown to advantage in FIG. 2, the outer sets of plates 1812band 18412 are offset upwardly from the inner sets of plates 182a and184a. All of the plates may be substantially rectangular, except thatthe plates preferably have slanting or tapered inner edges 186 and 188.

The capacitive coupling plates 182a, 182b, 184a, and 18% are adapted tomesh with inner and outer sets of movable tuning plates 192a, 192b, 194aand 194b, all of which extend vertically and are substantially parallelto one another. Provision is made for effecting relative movementbetween the tuning plates and the coupling plates. Thus, in thisinstance, the tuning plates 192a, 1921;, 194a and 1942: are mounted onan insulating block 196 which is secured to the underside of the movablecarriage 88, near the V-shaped guide groove 102.

The outer tuning plates 1932b and 19421 are oflset upwardly from theinner tuning plates 192a and 194a. In this way the outer tuning plates19212 and 1341) are adapted to mesh with the outer coupling plates 132band 18412, while being adapted to pass over the inner coupling plates182a and 184a, when the carriage 88 is translated to the right, as seenin FIG. 2. The inner tuning plates 192a and 194a are progressivelyunmeshed from the coupling plates 182a and 13411 as the carriage 38 istranslated to the right.

In the illustrated construction, a connection providing a small amountof inductance is employed between the outer sets of tuning plates 1192band 19421. This connection may take the form of a hairpin-shapedinduction loop Zlltl. The inductance of the loop 200 may be adjusted bybending it and by applying solder or the like to'the loop so as tobridge a desired portion of the loop. Such a mass of solder 202 isindicated in FIG. 6. In this case, the inner tuning plates 192a and 194aare connected together by means of a conductive strap or plate 2%.Although the inductance of the plate 294 is extremely low, it may causespurious resonances. To damp out any such resonances, a resistor 266 isalso connected between the inner tuning plates 192a and 194a, inparallel with the plate 204.

The oscillator 4 may utilize a conventional circuit, including a radiofrequency choke 208 connected between the cathode 162 and ground, andanother choke 219 connected between the plate 166 and a positive powersupply terminal 212, the negative terminal of the power supply beinggrounded. A bypass capacitor 214 may be connected between the terminal212 and ground. As shown in FIGS. 12 and 13, a grid biasing resistor 216is connected between the grid 164 and ground.

When the carriage 88 is moved as far as possible to the left, as seen inFIG. 2, the outer tuning plates 192i) and 1941b are fully meshed withthe outer coupling plates 1392b and 1841). Similarly, the inner tuningplates 192a and 124a are fully meshed with the inner coupling plates182a and 184a. This position of the carriage 88 represents the lowfrequency end of the tuning range. The approximately equivalent circuitof the oscillator for low frequencies is represented in FIG. 12. For thelow frequency portion of the tuning range, the principal branch of thetuned circuit between the grid 164 and the plate 166 comprises theinductances of the bars 168 and 170, represented by the inductanceelements L168 and L170 in FIG. 12. The elements L168 and L170 shouldalso be taken as including the inductances of the leads 174 and 176 andthe inductances of the plates 1821), 192b, 184b and 194b, all of whichare in series with the inductances of the bars 168 and 170. Theinductance of the loop 269 is also elfectively in series with theinductances of the bars 168 and 170.

Also in the series circuit are the variable capacitances between theplates 18212 and 19212, and between the plates 13 1b and 194b,represented respectively by variable capacitance elements 222 and 224 inFIG. 12. It will be realized that the inductive loop 200 is effectivelyconnected in series between the capacitance elements 222 and 224.

The variable capacitances between the plates 182a and 192a, and betweenthe plates 184a and 194a, are represented by variable capacitanceelements 226 and 228 in FIG. 12. These capacitance elements 226 and 228are effectively in series with the inductance 230 of the plate 204, andthe inductances 232 and 234 of the plates 182a, 192a, 184a, and 194a.All of these inductive elements are small so that the variablecapacitance elements 226 and 228 effectively provide additional shuntcapacitance between the grid 164 and the plate 166.

When the carriage 88 is translated to the right, the plates 192b and19412 are progressively unmeshed from the plates 182i) and 18411. Thisreduces the values of the capacitance elements 222 and 224. At the sametime, the effective inductance of the bars 168 and 170 is reduced by themovement of the plates 192b and 1941) to the right. Moreover, the innerplates 192a and 194a are progressively unmeshed from the plates 182a and184a, thus reducing the capacitance of the elements 226 and 228. All ofthese factors increase the resonant frequency of the tuned circuit 160.

When the carriage 88 is translated as far as possible to the right, asseen in FIG. 2, the tuner is adjusted to the high frequency end of itstuning range. The plates 192a and 194a are entirely unmeshed from theplates 182a and 184a, so that the variable capacitance elements 226 and228 are reduced to very low values, and hence are etfectively out of thetuned circuit 160.

' FIG. 13 is an approximately equivalent circuit diagram of theoscillator 4 for the high frequency end of the tuning range. In thisdiagram, the variable capacitance elements 226 and 223, the inductanceelement 230, and the resistor 206 are represented in broken lines,indicating that these components are effectively out of the tunedcircuit. The outer tuning plates 19% and 194% are also entirely unmeshedfrom the outer coupling plates 18% and 184b, .but the plates 19211 and1941) are spaced edgewise above the plates 182a and 1840. In FIG. 13,the edgewise capacitances between the plates 182a and 192b, and betweenthe plates 184a and 1941;, are represented by variable capacitanceelements 242 and 244, which are effectively in series with theinductance loop 209 and inductance elements 246 and 24-8, between thegrid 164 and the plate 166. The inductance elements 246 and 248represent the effective inductances of the leads 174 and 176, the innerbar portions 168a and 1700, and the plates 1820, 192b, 184a and 1941').All of these inductances are very small, so that the total inductance isgreatly reduced at the high frequency end of the tuning range. Theedgewise capacitances represented by the elements 242 and 244 are alsoquite small, so that the oscillator can be tuned to an extremely highfrequency of about 1,000 megacycles. In tuning the oscillator betweenthe low and high frequency ends of the tuning range, there is a gradualtransition between the conditions represented by FIGS. 12 and 13. Theresistor 206 damps out any spurious resonances in which the inductance230 of the plate 2%94 would play a part. Thus, the resistor 206contributes to the smoothness of the tuning variation and preventssudden jumps in the frequency of the oscillator.

Tracking adjustments may be made in the oscillator 4 in various ways.Thus, the inductance loop 200 may be bent, as desired, and may beelfectively shortened by applying solder thereto. The elevation of theplates 192, 1921), 194a, and 194i may be changed rather easily. Forexample, this may be done by placing shims between the insulatingsupport 196 and the various plate assemblies. If necessary, portions ofthe various plates may be bent.

As previously indicated, the mixer stage 8 utilizes a crystal diode 9having terminals 252 and 254. The incoming radio frequency signals areapplied to the diode 9 by means of the lead 58 connected between thepickup loop 56 and the terminal 252. The output from the diode 9 istaken. by an output lead 256 which is connected to the terminal 254through a radio frequency choke 258. A small capacitor 260 is providedbetween the terminal 254 and ground.

In accordance with another feature of the present invention, energy fromthe oscillator 4 is fed to the mixer diode 9 by means of an elongatedpickup conductor 262 which is disposed in proximity to the tuned circuit3.60 of the oscillator 4. In this case, the pickup lead 262 is disposednear the plates 184b. A current limiting resistor 264 is connectedbetween the lead 262 and the terminal 254 of the diode 9. To suppressany spurious resonances in the pickup lead 262, the lead is doubled backupon itself to form an elongated loop with a resistor 266 in seriestherewith. Because of the wide frequency range covered by the tuner, itis difiicult to avoid unwanted resonances in the pickup lead 262 but anysuch resonances are damped out by the resistor 266. In this way, theoscillator energy fed to the mixer diode 9 is maintained at a reasonablyuniform level throughout the tuning range.

It will be evident that the tuner of the present invention is highlyefiicient and versatile, yet is extremely small and compact. Theoscillator provides smooth and continuous coverage of an extremely widefrequency range. The preselector units 12a and 12b may be tracked veryaccurately to the desired tuning curve, established by the oscillatortuning, at a multiplicity of points through- 10 out the tuning range.With all its advantages, the tuner is remarkably low in cost.

Various other modifications, alternative constructions and equivalentsmay be employed without departing from the true spirit and scope of theinvention, as exemplified in the foregoing description and defined inthe following claims:

We claim:

1. In a tuner,

the combination comprising an oscillator device having first and secondterminals,

first and second generally parallel bars having inner end portionsconnected to the respective first and second terminals,

said bars having outer end portions offset laterally from said inner endportions,

each bar having inner and outer coupling plates mounted on said innerand outer end portions,

all of said plates on said first and second bars being substantiallyparallel,

said outer plates being offset in an edgewise direction with respect tosaid inner plates,

a carriage movable generally in a longitudinal direction with respect tosaid bars, first and second inner tuning plates mounted on said carriageand movable into overlapping relation with said respective first andsecond inner coupling plates,

insulating means mounting said inner tuning plates on said carriage,

a conductive member connected between said first and second inner tuningplates,

first and second outer tuning plates mounted on said carriage andmovable into overlapping relation with. said first and second outercoupling plates,

an outer inductance element connected between said first and secondouter tuning plates,

all of said tuning plates being substantially parallel to thecorresponding coupling plates,

and means for translating said carriage to move said inner and outertuning plates out of overlapping relation to said respective inner andouter coupling plates to reduce both the effective inductance of saidbars and the effective capacitance between said bars,

said outer inductance element effectively being in series with theinductance of said bars.

2. In a tuner,

the combination comprising first and second elongated generally parallelconductors having inner and outer end portions,

said outer end portions being generally parallel to said inner endportions but being offset laterally therefrom,

first and second terminals connected to said inner end portions of saidconductors,

first and second inner coupling plates connected to said inner endportions of said conductors,

first and second outer coupling plates connected to said outer endportions of said conductors,

all of said plates being generally parallel,

said outer plates being offset edgewise relative to said inner plates,

a tuning member,

means supporting said tuning member and said conductors for relativemovement between said tuning member and said conductors in a directiongenerally parallel to said conductors,

first and second inner tuning plates mounted on said tuning member andmovable into overlapping relation to said inner coupling plates,

first and second outer tuning plates mounted on said tuning member andmovable into overlapping relation to said outer coupling plates,

insulating means mounting said tuning plates on said tuning member,

an additional conductor connected between said first and second innertuning plates,

an inductance element connected between said first and second outertuning plates,

the inductance of said inductance element being effec tively in serieswith the inductance of said elongated conductors,

the relative movement between said tuning member and said conductorsbeing efiective to move said inner and outer tuning plates into and outof overlapping rela tion to said inner and outer coupling plates so asto vary both the effective inductance and the effective capacitancebetween said terminals.

3. In a tuner,

the combination comprising first and second generally parallel lineconductors,

each of said conductors having inner and outer end portions,

said outer 'end portions being oifset laterally relative to said innerend portions,

first and second terminals connected to said inner end portions of saidline conductors,

first and second inner coupling capacitance members mounted on saidinner end portions of said respective first and second conductors,

first and second outer capacitance coupling members mounted on saidouter end portions of said first and second conductors,

a tuning member,

first and second inner "tuning capacitance members mounted on saidtuning member and disposed in variable overlapping relation to saidrespective first and second inner coupling capacitance members,

first and second outer tuning capacitance members mounted on said tuningmember and disposed in variable overlapping relation to said respectivefirst and second outer coupling capacitance members,

conductive means connected between said first and second inner tuningcapacitance members,

an inductance element'connected between said first and second outertuning capacitance members,

and means supporting said tuning member and said line conductors forrelative movement between said tuning member and said line conductors ina direction generally parallelto said line conductors for thereby movingsaid inner and outer tuning capacitance members into and out ofoverlapping relation to said inner and outer coupling capacitancemembers so as to vary both the eltective inductance and the effectivecapacitance between said terminals.

ber for relative movement therebetween in a direction generally parallelto said conductors,

first and second inner tuning plates mounted on said tuning member andmovable into overlapping relation to said inner coupling plates,

first and second outer tuning plates mounted on said tuning member andmovable into overlapping relation to said outer coupling plates,

insulating means mounting saidtuning plates on said tuning member,

means connected between said first and second inner tuning plates,

means connected between said first and second outer tuning plates,

the relative movement between said tuning member and said conductorsbeing effective to move said inner and outer tuning plates into and outof overlapping relation to said inner and outer coupling plates so as tovary both the effective inductance and the effective capacitance betweensaid terminals.

3. IN A TUNER, THE COMBINATION COMPRISING FIRST AND SECOND GENERALLYPARALLEL LINE CONDUCTORS, EACH OF SAID CONDUCTORS HAVING INNER AND OUTEREND PORTIONS, SAID OUTER END PORTIONS BEING OFFSET LATERALLY RELATIVE TOSAID INNER END PORTIONS, FIRST AND SECOND TERMINALS CONNECTED TO SAIDINNER END PORTIONS OF SAID LINE CONDUCTORS, FIRST AND SECOND INNERCOUPLING CAPACITANCE MEMBERS MOUNTED ON SAID INNER END PORTIONS OF SAIDRESPECTIVE FIRST AND SECOND CONDUCTORS, FIRST AND SECOND OUTERCAPACITANCE COUPLING MEMBERS MOUNTED ON SAID OUTER END PORTIONS OF SAIDFIRST AND SECOND CONDUCTORS, A TUNING MEMBER, FIRST AND SECOND INNERTUNING CAPACITANCE MEMBERS MOUNTED ON SAID TUNING MEMBER AND DISPOSED INVARIABLE OVERLAPPING RELATION TO SAID RESPECTIVE FIRST AND SECOND INNERCOUPLING CAPACITANCE MEMBERS, FIRST AND SECOND OUTER TUNING CAPACITANCEMEMBERS MOUNTED ON SAID TUNING MEMBER AND DISPOSED IN VARIABLEOVERLAPPING RELATION TO SAID RESPECTIVE FIRST AND SECOND OUTER COUPLINGCAPACITANCE MEMBERS, CONDUCTIVE MEANS CONNECTED BETWEEN SAID FIRST ANDSECOND INNER TUNING CAPACITANCE MEMBERS, AN INDUCTANCE ELEMENT CONNECTEDBETWEEN SAID FIRST AND SECOND OUTER TUNING CAPACITANCE MEMBERS, ANDMEANS SUPPORTING SAID TUNING MEMBER AND SAID LINE CONDUCTORS FORRELATIVE MOVEMENT BETWEEN SAID TUNING MEMBER AND SAID LINE CONDUCTORS INA DIRECTION GENERALLY PARALLEL TO SAID LINE CONDUCTORS FOR THEREBYMOVING SAID INNER AND OUTER TUNING CAPACITANCE MEMBERS INTO AND OUT OFOVERLAPPING RELATION TO SAID INNER AND OUTER COUPLING CAPACITANCEMEMBERS SO AS TO VARY BOTH THE EFFECTIVE INDUCTANCE AND THE EFFECTIVECAPACITANCE BETWEEN SAID TERMINALS.